As it is known, in the current state of art the austenitic steels can be schematically separated into two large families: stainless austenitic steels (AISI200 and AISI300 series type) and steels with high content of Mn (Mn>11% by weight).
The austenitic steels with high Mn content (Hadfield type and TWIP steels) are steels wherein the stabilization of the austenitic structure is obtained by means of suitable additions of Mn and C. The TWIP austenitic steels with high Mn, Fe-22Mn-0.6C or Fe-22Mn-3Al-3Si type, constitute an independent family of steels in the field of the high resistant steels as they have definitely peculiar mechanical properties (UTS 700-1000 Mpa) and they are characterized above all by very high ductility (A80>60%) and work hardening. These steels have an austenitic structure with face-centered cubic lattice (FCC), together with a low energy of the stacking fault (SFE) promoting the activation of the deformation mechanisms by twinning (twinning induced mechanically).
In the last decade the TWIP steels have been object of an intense research activity as they are considered extremely interesting for the applications wherein high performances in terms of ductility, capability of hardening and energy absorption during deformation are requested (WO99/01585, EP0889144).
A limit of this typology of steels (TWIP with high Mn) is the poor resistance to corrosion thereof; for the application in the automotive field and more in general in all fields wherein the steel is exposed to a not protected and potentially corrosive environment, there is the need for protecting the steel by means of coating such as galvanizing. The problems of the zinc layer adhesion make the electrogalvanising process (EG) the most suitable one for the TWIP steels with high Mn.
In the state of art (WO2006/025412, US2012/0000580A) there are some proposals trying to obtain corrosion-resistant TWIP steels obtained by adding about 12% of Cr to the composition of the TWIP steel with high Mn. These variants have a chemical composition of the Fe-25Mn-12Cr-0.25C-0.3N type and they have not high level of resistance to corrosion and are not suitable to relatively corrosive environments.
A process for the industrial implementation of a high-resistant stainless steel (UTS>700 MPa), with high ductility (A80>80%), which at the same time is suitable for applications in corrosive environments, is not yet known to the state of art. Therefore, in different industrial fields, there is the need for having available a stainless steel able to offer an optimum compromise between cost of manufacturing cycle and mechanical properties, resistance to corrosion and high formability together with a good surface quality.
The TWIP austenitic steels with high Mn, apart from the poor resistance to corrosion and the difficulties linked to the galvanizing process, have additional criticalities linked to the manufacturing cycle, with high manufacturing costs, which strongly hinder the industrialization thereof, and therefore the application in fields such as the automotive one. Substantially, the most critical aspects are the following ones;                ferro-alloy cost;        hydrogen embrittlement (RFSR-CT-2005-00030, WO2012/07715A2);        high resistance to hot and cold deformation;        environmental problems in steel works linked to the high Mn content.        